The present invention pertains to the field of electro-optical devices including field emission devices and to a method for fabricating such devices.
Photoconductive imaging devices, such as camera vacuum tubes and charge couple devices (CCDs) are well known in the imaging field. In general, a camera tube is an image pick-up tube that includes a photoconductive layer which acts as the photosensitive surface. A wide variety of camera tube types are manufactured, each having unique characteristics. Generally, the type of tube selected is based on the need to balance resolution, integration (lag) and contrast. All of these imaging devices have one thing in common, they require a vacuum tube imager to convert reflected light into electrical impulses.
This is accomplished by firing a steady stream of high-velocity electrons at the back side of a CRT-type imager. Vidicon camera tubes are the most well known type of camera tube and have been found to work best in environments where there is full, consistent light. Generally a Vidicon camera tube offers good resolution, moderate lag, and low image distortion. On the negative side, Vidicon camera tubes, and vacuum tubes utilized for imaging in general, are bulky and have a thermionic cathode.
CCD imaging devices on the other hand, are made using a semiconductor target instead of a vacuum tube. CCDs are typically designed to satisfactorily collect images in environments where the light level is low-to-full and somewhat variable. Each element in a CCD stores a charge that is determined by the illumination incident on it. At the end of the exposure interval, the charge is transferred to a storage register and the CCD is freed up for the next exposure. The charges in the storage register are transferred to the output stage serially during that time. The advantage that a CCD model realizes over that of a tube-type imaging devices lies in how the image scenes are formed. Because there is a semi-conductor instead of a tube in these devices, they are not susceptible to many of the same problems, such as bulkiness and image bloom. In addition, because CCDs generate less heat within them, the electronic components found inside last longer. Yet negative aspects to the CCD imaging device exist in the form of relatively low sensitivity to light and limited environmental capabilities.
In addition, field emission arrays (FEAs) have been known for many years. FEAs typically use a structure commonly known as a Spindt tip as an emitter or carbon nanotubes. FEAs further include an anode which collects electrons emitted by the emitters and is disposed within 200-5000 micrometers from a plurality of gate extraction electrodes positioned proximate the emitters. Field emission camera tubes have been reported, yet these devices fail to overcome the defects previously mentioned with regard to camera tubes and CCDs.
Accordingly, it is highly desirable to provide a device which overcomes these problems currently found with imaging devices and a method of fabricating the device. Thus, there exists a need for an improved imaging device which is simple to fabricate, compact, has a high light sensitivity, is simple to address, and has a potentially long life.